Method of finishing metal surfaces



Nov. 5, 1957 J. D. PATRICK 2,812,295

METHOD OF FINISHING METAL SURFACES Filed March 22, 1955 FORM PATTERN lNMETAL :C AN.

RINSE CHEMICAL BRIGHTENER RINSE i ANODIZE RINSE T FIRST DYE RINSE ANDDRY' APPLY STOP OFF I COATING SECOND DYE REMOVE STOP OFF COATING SEALINVENTOR. Jam es 0. Parr/ck 'H/s Afro/way United States Patent Ofihce2,812,25 Patented. Nov. 5, lfiii? METHOD OF FINISHING METAL SURFACESJames D. Patrick, Dayton, Ohio, assignor to General Motors Corporation,Detroit, Mich, a corporation of Delaware Application March 22, 1955,Serial No. 495,898

2 Claims. (Cl. 204-48) This invention relates to the manufacture ofdecorative surfaces and in particular to multi-colored surfaces formedon metal by means of successive dyeing of .anodized metal surfaces.

It is well known that various'metals, as, for example, aluminum, may beanodized to form an oxide film on the surface thereof which in turn maybe colored by various dyes. Various methods have also been developed forcreating multi-colored effects on metal surfaces which involve dyeingonly selected portions of anodized metal surfaces. In one method the wetanodic film is immersed in a solution of antimony potassium tartrate andthen in ammonium sulfide whereby a skin of antimony sulfide is formedover the anodic film. The thin sulfide film is then broken and immersedin a dye solution whereby the dye penetrates the anodic film at thepoints Where the sulfide film is broken. In subsequent operations otherportions of the sulfide film are broken and the exposed anodic film isdyed. In another method, precise designs are stopped off on the anodicfilm prior to dyeing by means of lithographers ink or cellulose lacquereither by means of an offset printing press, silk screen or by sprayingthrough a stencil. In one method portions of the anodic surface arestopped off by a colored wax and the balance of the film is dyed in acontrasting color. In some methods, portions of a dyed anodic film arebleached and the bleached portions are dyed another color. In anothermethod, the anodic film is coated with a metal film by metal evaporationafter which portions of the metal are coated with an acid resistingcompound and the unprotected metal is etched away to expose the anodicfilm which is then dyed. The various methods of creating multi-coloredeffects on metal surfaces involving dyeing of anodic film which areknown to the inventor as, for example, those mentioned above, arerelatively complicated and/or are lacking in permanence and durability.

It is accordingly an object of this invention to provide a relativelysimple and inexpensive method of forming variegated metal surfaces whichconsists in providing an uneven or pattern configuration having raisedand depressed portions in the surface of the metal, anodizing thepattern surface and dyeing the raised portions of the surface adifferent color or shade than the depressed portions.

It is a further object of this invention to provide a method forproducing decorative variegated metal surfaces wherein an uneven orpatterned surface having raised and depressed portions is formed in themetal surface, the surface is anodized, and the raised and/or depressedportions are subjected to one or more dyeing operations and raised ordepressed portions are coated with a substance impregnable to Waterbefore or between dyeing operations whereby raised and/or depressedportions are selectively dyed.

Another object of this invention is to provide a method of formingvariegated metal surfaces which consists in providing a metal surfacewith raised and depressed portions, anodizing the metal surfaces, dyeingthe metal surface a first shade or color and thereafter coating raisedor depressed portions with a substance impregnable to water andsuccessively bleaching and dyeing uncoatcd surfaces whereby the raisedand depressed portions are selectively dyed.

Further objects and advantages of this invention will be apparent fromthe following description, reference being had to the accompanyingdrawings wherein preferred embodiments of the present invention areclearly shown.

In the drawings:

Figure 1 is a flow chart showing major steps in forming a decorativesurface in accordance with the present invention.

Figure 2 is an enlarged cross sectional view of a decorative metal panelhaving stop off material applied to the raised portions of the surface.

The invention will be described in terms of a specific example althoughit will be obvious that the basic method has broad application.

A metal article is first provided with an uneven or patterned surfacehaving raised and depressed portions. In the specific example to bedescribed, a pattern is rolled or stamped into the surface of analuminum sheet. However, the patterned surface may be formed by anymethod and the invention is applicable to any metal capable of beinganodized.

The aluminum panel is then immersed in an alkali cleaning bath of aconventional type as, for example, a solution of trisodium phosphate tofree the patterned surface of grease and other extraneous materialswithout substantially etching the surface thereof.

The clean panel is then dipped in a brightening bath. This step isdesirable since commercial grade of sheet, strip stock, etc. is notsmooth enough to present a polished bright surface. The brightening bathoperates to level the metal surface and provide a polished brightappearance. Suitable brightening baths include phosphoric acid andnitric acid in various proportions with or without sulphuric acid andnitric acid-hydrofluoric acid. The choice of brightening bath and itsconcentration and operating temperature will, of course, be made inaccordance with the kind of metalto be brightened and the specificresults desired as is well known in the art. This step is important inthat it markedly influences the color of the final product.

After water rinsing the metal free of brightening bath solution, themetal surface is then anodized. Suitable results are obtained using a15% sulphuric acid solution at F. with a current density of from toamperes a minute per square foot wherein an anodic coating in the orderof .0001" to .0003 thick is obtained. Other anodizing methods using, forexample, chromic and phosphoric acid baths may be employed as is wellknown in the art. Anodic films having a thickness in the vicinity of.0003 are preferred as anodic coatings of this thickness producesuperior light fast colors on dyeing as compared to thinner coatings.

The anodized surface is then water rinsed free of the anodizing acidbath and immersed in a suitable aqueous dye solution. Any of the dyesconventionally used to dye anodic films may be used which produce colorsof light fastness and which may be used at temperatures which will notresult in a sealing of the anodic film. Examples of suitable dyes whichmay be used are those of the Neolan series and the oxanol group.

The metal article is then water rinsed and dried, and the raisedportions of the dyed metal surface are coated. This operation may bereadily accomplished by merely brushing a cloth containing suitable stopoff material over the surface of the pattern or by the use of a rubberroller. The stop off material may be any relatively viscous substancewhich is readily applied but which will not readily flow into thedepressed portions of the pattern on application to the surface of thepattern and which will serve to prevent the penetration of water to theanodic layer. Examples of suitable substances which may be used includeoil, wax and printers ink.

Figure 2 shows in enlarged cross section a metal panel ill havingthereon a patterned surface, an anodic 12 on the pattern metal surfaceand oil or wax coating 14 applied to high spots or raised portions ofthe panel which has been applied as above described. As indicated above,a feature of the present invention is its simplicity whereby complicatedand expensive methods of coating portions not to be dyed are eliminatedin producing attractive variegated metal surfaces. Where relativelylarge panels are to be formed, the coating substance may be convenientlyapplied as, for example, by rubber or fibrous rolls as areconventionally used in painting walls and the like. Further, such rollsmy be readily used in mechanical devices whereby mass production methodsmay be applied.

After application of the coating material the panel is again subjectedto a dye whereby additional dye is absorbed by the uncoated or depressedportions of the panel. After conclusion of the second dyeing operation,the stop ofi material is removed and the anodic film may then be sealedby immersing it in hot water maintained in the neighborhood of 200 F. asis well known in the art whereby the anodic film becomes hydrated andseals the dye in the anodic pores. Sealing in the presence of nickelacetate may be employed to help fix the dye. Alternatively, the dyedanodic film may be sealed by exposing it to steam as is well known inthe art.

The method above described is effective in producing variegated surfaceshaving depressed pattern portions of relatively darker color than theraised pattern portions. A variation of this method may be used tocreate patterns having darker raised portions than the depressedportions. The anodized metal surface is first dyed a relatively darkercolor, raised portions are coated as previously described and thearticle is immersed for a few seconds in an acid bath which in effectbleaches the depressed portions of the pattern. Suitable acid bathsinclude hydrochloric acid, nitric acid and sulfuric acid-nitric acidsolutions. The article is then rinsed and immersed in a dye solution oflighter or second color whereby only the depressed portions of thepattern are dyed. The coating substance is then removed and the dyedsurfaces are sealed. This variation not only permits a darker color butalso a truer color on the depressed portions of the pattern since onlysingle colors are applied to both depressed and raised portions.

The method of the present invention permits many variations. Forexample, the coating substance may be applied to both raised anddepressed portions and then wiped off the raised portions by merelywiping the surface of the metal with a dry cloth or other suitable meanswhereby the raised portions only may be successively dyed. Where themetal has a naturally attractive color as, for example, aluminum, raisedportions may be undyed and only depressed portions may be dyed bycoating the raised portions prior to a dyeing treatment. Similarly, onlyraised portions may be dyed by coating depressed portions, as aboveindicated, prior to a dyeing treatment.

A variety of color effects may be obtained by the choice of dyes, thelength of the first dyeing operation and the length of the second dyeingoperation. For example, the dye may be of copper color and in the firstdyeing operation, a relatively light shade may be obtained. The same dyemay be applied in the second dyeing operation for a substantially longerperiod of time than in the first dyeing operation whereby the resultingfinish consists of raised portions having a light copper color and thedepressed portion a darker copper color. In another variation, thesecond dyeing operation may involve a different or dark dye such asblack whereby the resulting finish consists of raised portions of coppercolor and depressed portion of a black color. Besides, the choice ofdyes and the length of the dyeing operation, the dye bath operatingconditions and the character of the brightening finish may all be variedto produce various effects. Conversely, these factors must be carefullycontrolled to secure uniform results in processing a batch of panels ifidentical panels are to be expected. It is obvious that the nature ofthe configuration of the uneven or pattern surface influences the natureof the finished product. Thus, if the raised surfaces of the metal breaksharply with the depressed portions, the depressed portions of one colorwill be clearly defined from the raised portions of another color.Conversely, if the surface of the raised portions joins the surface ofthe depressed portions by more or less gently curved surfaces, the colordefinition will be less uniform and clear. To attain certain effects, itmay be desirable to subject the anodized film to more than two dyeingoperations and more than two dyes. The above described method isintended to described the basic features of the invention. It is obviousthat the basic method may be modified in various ways without departingfrom the spirit of the invention.

While the embodiments of the present invention as herein disclosed,constitute preferred forms, it is to be understood that other formsmight be adopted.

What is claimed is as follows:

1. In a method for making multi-colored designs upon a sheet ofanodizable metal, said design having sharply defined boundaries betweenadjacent color areas, the steps comprising; forming a pattern havingsharply defined raised portions and depressed portions in the surface ofa sheet of anodizable metal, cleaning said surface, anodizing said metalsurface, dyeing the anodized surfaces in a solution of soluble organicdye, applying a relatively viscous substance over said raised portionswhich is impregnable to water, said substance being of sufficient viscosity so that on application to said raised portions it will not flowbeyond the sharply defined edges thereof, immersing said anodizedsurfaces in a solution of soluble darker and different organic dye thanthe first said dye, and removing said coating substance and sealing saiddyes Within the pores of said anodized surfaces.

2. In a method for making multi-colored designs upon a sheet ofanodizable metal, said design having sharply defined boundaries betweenadjacent color areas, the steps comprising; forming a pattern havingsharply defined raised portions and depressed portions in a metalsurface, anodizing the metal surface, dyeing the anodized surface arelatively dark color by immersion in a solution of organic dye,applying a relatively viscous substance which is impregnable to waterand acid to said raised portions, said substance being of sufficientviscosity so that an application to said raised portions it will notflow beyond the sharply defined edges thereof, immersing said anodizedsurfaces in an acid solution capable of bleaching the dyed anodizedsurfaces whereby only said depressed portions are bleached, dyeing thebleach anodized surfaces a relatively lighter color than said raisedportions by immersion in a solution of soluble organic dye.

References Cited in the file of this patent UNITED STATES PATENTS378,442 Hafely Feb. 28, 1888 2,010,336 Strassner Aug. 6, 1935 2,127,885Pettit Aug. 23, 1938 2,683,113 France et al. July 6, 1954 OTHERREFERENCES The Metal Industry, Production of Multi-Coloured Efiects onAnodised Aluminum, June 18, 1943, pp. 386-

1. IN A METHOD FOR MAKING MULTI-COLORED DESIGNS UPON A SHEET OFANODIZABLE METAL, SAID DESIGN HAVING SHARPLY DEFINED BOUNDARIES BETWEENADJACENT COLOR AREAS, THE STEPS COMPRISING; FORMING A PATTERN HAVINGSHARPLY DEFINED RAISED PORTIONS AND DEPRESSED PORTIONS IN THE SURFACE OFA SHEET OF ANODIZABLE METAL, CLEANING SAID SURFACE, ANODIZING SAID METALSURFACE, DYEING THE ANODIZED SURFACES IN A SOLUTION OF SOLUBLE ORGANICDYE, APPLYING A RELATIVELY VISCOUS SUBSTANCE OVER SAID RAISED PORTIONSWHICH IS IMPREGNABLE TO WATER, SAID SUBSTANCE BEING OF SUFFICIENTVISCOSITY SO THAT ON APPLICATION TO SAID RAISED PORTIONS IT WILL NOTFLOW BEYOND THE SHARPLY DEFINED EDGES THEREOF, IMMERSING SAID ANODIZEDSURFACES IN A SOLUTION OF SOLUBLE DARKER AND DIFFERENT ORGANIC DYE THANTHE FIRST SAID DYE, AND REMOVING SAID COATING SUBSTANCE AND SEALING SAIDDYES WITHIN THE PORES OF SAID ANODIZED SURFACES.